1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) and, more particularly, to a side type LED LCD device capable of improving motion blur of video and sharpness of an image using a prism light guide panel.
2. Description of the Related Art
The importance of the display industry has increased along with the rapid development of the information communication sector. While CRTs (Cathode Ray Tubes) have long been employed to display images, the display industry has extended its reach into application fields including aircrafts and spacecrafts. Accordingly the demand for large, portable displays with high resolution has increased.
For example, currently manufactured or developed flat panel displays include the LCD (liquid crystal display), the ELD (Electro Luminescent Display), the FED (Field Emission Display), and the PDP (Plasma Display Panel). An ideal flat panel display would be light in weight, and would have high luminance, high efficiency, with high resolution and fast response time characteristics. The ideal flat panel display would also implement low-voltage driving, have low power consumption, be low in low cost, and display natural colors. Among the flat panel displays, the LCD has received much attention because of its advantages of durability and portability.
Because the LCD is not a self-emissive device, LCDs require a backlight unit providing a light source to illuminate the liquid crystal panel that displays an image according to information received from an external system. The CCFL (Cold Cathode Fluorescent lamp) and an LED (Light Emitting Diode) are among the typically used light sources.
Backlight units are characterized as side type backlight units or direct type backlight units depending on the disposition of the light source. Here, the side type backlight unit, in which the light source is disposed at the side portion of a light guide panel, is commonly employed for a small or medium model such as monitors of notebook computers or desktop computers, and the direct type backlight unit is commonly employed for the medium model such as the monitors of desktop computers or a large model such as TVs.
Side type backlight units are further divided into edge type backlight units in which at least one fluorescent lamp serving as a light source is positioned only at one side and plate type backlight units in which at least one fluorescent lamp is provided at both sides thereof. The edge type backlight unit is employed for the monitors of the notebook computers and the plate type backlight unit is employed for the monitors of the general desktop computers.
FIG. 1 an exploded perspective view of the general side type LED LCD in which the LED, a light source, is disposed at the side of the light guide panel.
As shown in FIG. 1, a reflective plate 21 that reflects light emitted from a light emitting unit, for example, a light emitting element such as the LED, to a liquid crystal panel 40 is attached on a lower cover 10, and metal PCBs 20 on which LEDs are fixedly arranged at uniform intervals and a light guide panel 24 are provided on the reflective plate 21.
The metal PCBs 20 are attached on an inner side of a surface curved upwardly from both edges of the lower cover 10, and in order to apply voltages to the LEDs fixed on the PCBs 20, the voltages supplied from a system external to the LCD are applied via holes formed at both corner portions of a bottom surface of the lower cover 10 to portions of positive (+) and negative (−) electrodes formed on the metal PCBs 20.
When the metal PCB 20 with the LEDs are attached to the side portions of the lower cover 10, light emitting units of the LEDs point toward the light guide panel 24, so light emitted therefrom is naturally introduced to the light guide panel 24.
Optical sheets 26 and 28 are stacked on the metal PCB 20 and the light guide panel 24 provided on the lower cover 10. The optical sheets 26 and 28 refer to two diffusion sheets 26 that diffuse light provided from the reflective plate 21 and the light guide panel 24 so as for the light to be irradiated to the liquid crystal panel 40, and two protection sheets 28 that protect the diffusion sheets 26.
A panel guide 30, a frame mold product, is positioned at an outer edge of the lower cover 10 in order to maintain the balance of overall power of the LCD and separate the liquid crystal panel by a certain interval.
The liquid crystal panel 40 for displaying an image is provided on the panel guide 30. The liquid crystal panel 40 includes a thin film transistor (TFT) array substrate and a color filter substrate that are attached in a facing manner with a uniform cell gap maintained therebetween, and liquid crystal injected between the two substrates.
An upper cover 50 in a rectangular frame shape that covers the edges of the liquid crystal panel 40 is assembled and fastened to the panel guide 30.
In the LCD having the side type LED backlight having such a structure as described above, a motion blur phenomenon occurs wherein motion is blurred when displaying video. Thus a scan driving method has been proposed.
FIG. 2 shows a simulation of the light propagation state when the LCD is scan-driven.
It is noted that when the LEDs constituting the backlight of the LCD are divided into a plurality of groups and scan-driven, light propagates (or diffuses) to the periphery of the light guide panel at the time of scanning driving in a particular region.
This phenomenon reveals that the LCD having a backlight of the related art has not been sufficiently improved by scan driving to improve the motion blur in displaying video. The related art backlight fails to meet the demands of consumers and the requirements of buyers.
An LCD having the side type LED backlight with a divisional light guide panel has been proposed as a solution, in which a backlight is scan-driven and has a structure to address the motion blurring problem.
FIG. 3 is an exploded perspective view showing the backlight structure of the side type LED LCD having a divisional light guide panel according to the related art.
As shown in FIG. 3, the backlight structure of the side type LED LCD with the divisional light guide panel includes a plurality of light guide panels 91a to 91d divided into four regions to perform field sequential (FS) driving, a lower reflective plate 92 provided at a lower side of the light guide panels 91a to 91d, and PCBs 94 fixed at both sides of the light guide panels 91a to 91d, on which a plurality of LEDs 93 are disposed.
The LEDs 93 provided on the PCBs 94 are divided into a light emitting part 93a and a body part 93b, respectively.
A plurality of dot patterns (not shown) are printed on a lower surface of the plurality of light guide panels 91a to 91d. 
With the backlight unit having such configuration, the first to fourth light guide panels 91a to 91d are sequentially driven, and light made incident on each light guide panel from the LEDs 93 is totally reflected therein by the index of refraction of air, so that light propagation to an ambient light guide panel other than one corresponding to the driving region can be suppressed.
However, assembly of the plurality of light guide panels of the backlight unit with the above described configuration is cumbersome and requires a relatively large assembly time.
FIG. 4 is an exploded perspective view showing a direct type LED LCD of the related art.
As shown in FIG. 4, a direct type LED backlight unit is provided on a lower cover 130 to provide light to the liquid crystal panel 110. A first reflective plate (not shown) that covers the entire surface of the lower cover 130 is first attached on the lower cover 130.
A plurality of metal PCBs 132 are arranged at uniform intervals on the lower cover 130 with the first reflective plate attached thereon.
The metal PCBs 132 are sorts of metal bars. R (red), G (green), and B (blue) LEDs 134a, 134b and 134c as a string and a conductive pattern for driving the R, G, and B LEDs 134a, 134b and 134c are formed on a front surface of the metal PCBs 132. A metal material for improving a problem of generation of heat of high temperature related to the R, G and B LEDs 134a, 134b and 134c is formed on a rear surface of the metal PCBs 132.
A second reflective plate (not shown) is attached on the respective PCBs 132.
At an upper side of the metal PCBs 132, there are formed a diffusion plate 141 and a diffusion sheet 142 that diffuse light emitted from the R, G and B LEDs 134a, 134b and 134c, a prism sheet 144 that increases luminance of light which has transmitted through the diffusion plate 141 and the diffusion sheet 142, and a protection sheet 146 that protects the prism sheet 144.
A main support 150 is provided at an upper side of the backlight. The main support 150 is a mold product made of a synthetic resin or stainless steel in a rectangular frame shape and maintains an overall power balance of the LCD.
The liquid crystal panel 110 is stacked on the main support 150 to receive light from the lower backlight to display data information from the external. The liquid crystal panel 110 includes a TFT array substrate on which a TFT, a switching element, is installed at each unit pixel, a color filter substrate including color filters for expressing color, and liquid crystal injected between the two substrates.
The upper cover 160 covers the edges of four sides of the liquid crystal panel 110 and assembled and fastened to the main support 150 and the lower cover 130.
The direct type LED LCD illustrated in FIG. 4 can be driven in a scanning manner and also can be driven in a divisional manner such that backlight driving of a brighter portion and a darker portion can be partially controlled according to an image of the LCD, whereby the contrast ratio can be increased on the entire screen to thus improve sharpness of picture quality.
However, because, the direct type LED LCD includes a large number of LEDs on the lower cover to obtain uniform luminance, the display has relatively large amounts of power.